Clay/Polymer Nanocomposites: Processing, Properties, and Applications

Abstract

Clay/polymer nanocomposites have been extensively studied in recent years. The present state of the art for these materials is summarized in this chapter. The development of fabrication methods for these composites is very challenging because the platelets of nanoclay exist in the form of clusters, which need to be dispersed in the matrix resin in order to obtain any benefit from the high surface area of nanoclay. Incorporation of only a small weight fraction (1–5 %) of nanoclay in polymers provides significant benefits in the properties of composites. Several tensile, flexural, and thermal properties are found to increase by 30–40 % due to the presence of nanoclay in the composite compared to the properties of the neat resin. Entrapment of air porosity at higher nanoclay content can lead to reversal of the trends and can actually reduce the mechanical properties of nanocomposites. Theoretical models have been developed to estimate the properties of nanocomposites by accounting for the microstructure that may include clustered, intercalated, or exfoliated nanoclay. The benefit in mechanical properties obtained from incorporating nanoclay is much greater than that can be achieved with microscale reinforcement at the same loading levels. The current applications of clay/epoxy nanocomposites are in the area of automotive moldings and fire retardant coatings.

Summary

Low cost and abundant availability of clay have been viewed as significant advantages in favor of developing high performance clay/polymer nanocomposites. Both thermoplastic and thermosetting resin matrix nanocomposites have been studied in the existing literature. The layered structure of clay can be exfoliated to create enormous surface area where matrix resins can be bonded to provide nanocomposites with increased mechanical properties. However, the dispersion of nanoclay is difficult and expensive. Several mechanical and chemical processes have been developed to effectively exfoliate nanoclay and obtain high quality composites. However, a review of existing data reveals that the potential of clay/polymer nanocomposites has not been fully realized and most properties are improved by 30–40 % compared to those of neat resin. Such improvement is obtained at low nanoclay content in the composites (1–5 wt %). At higher nanoclay loading levels, the exfoliation becomes progressively more difficult and entrapment of air in the composite during the mixing process increases and the advantages in the mechanical properties diminish. Tensile, flexural, and thermal properties of nanocomposites have been extensively studied in the available literature. Several innovative modeling approaches are now available in the literature. One of the main challenges for these schemes is to account for the presence of clustered, intercalated, and exfoliated nanoclay contents. The estimated properties are found to be within Hashin–Shtrikman bounds for the nanocomposites.

Industrial applications exist for clay/epoxy nanocomposites, while some new applications are also being exploited. Clay/epoxy nanocomposites provide improved corrosion protection, so that it might find applications in modern aircraft anticorrosive coatings (Tomić et al. 2014). Clay/epoxy nanocomposites have been widely used for structural adhesive applications, because of its potential to improve adhesive performance, practicality, and lower cost (Sancaktar and Kuznicki 2011). Most of the current applications are in automobiles, which now extensively use polymers inside the vehicle. Dashboards, parts of seat structures, and fixtures are examples of current applications. New applications are continuously being developed for nanoclay composites.